The invention relates to a feed device for supplying solid urea granules into an ammonia generator disposed within or outside of an exhaust line.
It is known to treat the exhaust of diesel engines by means of selective catalytic reduction (SCR) for the reduction of NOx. As reduction means for this purification process, ammonia is used, which can be produced in various ways within or outside of the exhaust line. The starting material for this can be solid urea or a urea solution.
EP 0487886 discloses a method for converting a urea solution by hydrolysis into ammonia and carbon dioxide.
EP 0615777 B1, in contrast, discloses a method in which solid urea particles are converted into ammonia, which is then processed in the scope of exhaust post-treatment to nitrous oxide reduction. For supply of the solid urea particles, a holding tank for the particles and a specialized metering device are provided. In this connection, a motor-driven worm conveys the supplied urea particles into a line impinged with compressed air, in which they are carried away and supplied to a hydrolytic catalytic converter. One disadvantage of this solution is the poor meterability of the amount of the urea particles and the high consumption of compressed air.
With another similar solution disclosed in DE 10252734 A1, solid urea prills on the end of a conveyor, in which they are moved by means of a motorized worm to a crushing device, are crushed by rotating vanes or blades. These vanes or blades are also a part of a blower and produce an air flow in its housing, with which the crushed urea particles are conveyed via a tube into an exhaust line.
Although with this solution, no independent compressed air source is required, it is not completely satisfactory, because it permits only a relatively rough metering of the urea prills.